Upload
others
View
2
Download
0
Embed Size (px)
Citation preview
Aq-Ai63 571 SUBSEA CABLE BURIAL SYSTEM OUTLINE OF CONCEPTUAL DESIGN iA~(U) NAVAL FACILITIES ENGINEERING COMMAND WASHINGTON DC
* CHESAPEAKE DIV M MELL OR DEC 76 CHES/NAVFRC-FPO-7682
NCLASSIFIED F/G 13/9 NI
EElIIII~lllhEIIhhh~EEl
m11 1.2 1102.... -.
I .
11111-25 .4 11 .6
MICROCOPY RESOLUTION TEST CHARTNATIONAL BUREAU OF STANDARS 19G63 -A
0
SM
FPO -7602 - -
In
SUBS;EA CABLE BUEIAL SYSTE'!
* OIJTLI .2: 07 C0:;CiTTUALIT. s :
TD
.~ i
~Lip
~of
UnclassifiedSECURITY CLASSIFICATION OF THIS PAGE
REPORT DOCUMENTATION PAGEla. REPORT SECURITY CLASSIFICATION lb. RESTRICTIVE MARKINGSUnclassified
2a. SECURITY CLASSIFICATION AUTHORITY 3. DISTRIBUTION AVAILABILITY OF REPApproved for public release;distribution is unlimited
2b. DECLASSIFICATION/DOWNGRADING SCHEDULE
4. PERFORMING ORGANIZATION REPORT NUMBER 5. MONITORING ORGANIZATION REPORT #FPO 7602
6a. NAME OF PERFORM. ORG. 6b. OFFICE SYM 7a. NAME OF MONITORING ORGANIZATIONUSACRREL Ocean Engineering
& ConstructionProject OfficeCHESNAVFACENGCOM
6c. ADDRESS (City. State, and Zip Code) 7b. ADDRESS (City. State, and Zip )BLDG. 212, Washington Navy Yard
* Washington, D.C. 20374-21218 Ba. NAME OF FTUDTNG ORG. 8b. OFFTCE SYM 9. PROCUREMENT INSTRUMENT INDENT #
8c. ADDRESS (City. State & Zip) 10. SOURCE OF FUNDING NUMBERSPROGRAM PROJECT TASK WORK UNITELEMENT # 0 * ACCESS #
11. TITLE (Including Security Classification)Subsea Cable Burial System Outline of Conceptual Design
12. PERSONAL AUTHOR(S)Malcolm Mellor13a. TYPE OF REPORT 13b. TIME COVERED 14. DATE OF REP. (YYMMDD) 15. PAGES
FROM TO 76-12 2616. SUPPLEMENTARY NOTATION
17. COSATI CODES 18. SUBJECT TERMS (Continue on reverse if nec.FIELD GROUP SUB-GROUP ,- Cable; Cable Installation; Retreival 4-&
, Repair _
- 19. ABSTRACT (Continue on reverse if necessary & identify by block number)The goal is to bury undersea cable in various kinds of bed material, includinghard bottom. It is desirable to have a self-contained ma:hine that canoperate across beaches, through the surf zone, and along the sea bed to the150 ft. water depth. Ksf'c ,'i..20. DISTRIBUTION/AVATLABILITY OF ABSTRACT 21. ABSTRACT SECURITY CLASSIFICATIO
* SAME AS RPT.22a. NAME OF RESPONSIBLE INDIVIDUAL 22b. TELEPHONE 22c. OFFICE SYMBOLJacqueline B. Riley 202-433-3881DD FORM 1473, 84MAR SECURITY CLASSIFICATION OF THIS PAGH
1(2)
SUBSEA CABLE BURIAL SYSTEM
OUTLINE OF CONCEPTUAL DESIGN
OTICSELECTElFEBO 3 MO8D
MALCOLM MELLOR
USACRREL
for
NAVAL FACILITIES ENGINEERING COMMAND
DITIUINSTATEMENIT A 86 2 a3 0 1 8Aj~roved for public releci
Diatibutiorn Unlimited NDecembr 197
- ? ~r
Contents
Problem definition 1
Outline of System and Functions 1
Design Constraints 3
Penetration of the Bed Material 3
Material Removal 4
Laying in the cable 5
Propulsion of the carrier vehicle and burying unit 7
Power transmission 8
Final drives 8
Control, Guidance and Monitoring 9
Selection of Subsystem Concepts 10
Summary and Conclusions 18
* v Attachment #1
Accesion For
NTIS CRA&IDTIC TABUnannounced 0J Jstification ...........
By ......................................... .ODi-t ibjtion I
Availability CodesC
Distj Avail ar.d /orSpcial
* A-1I1V
SUBSEA CABLE BURIAL SYSTEM
CONCEPTUAL DESIGN
Problem definition
At the inception of this project, the problem was defined in
the NAVFAC Statement of Work, and performance requirements were
subsequently reviewed as the first stage of the work. However,
more recent discussions, especially those held at the Naval Civil
Engineering Laboratory in Port Hueneme, have changed our perception
of the problem. In particular, it seems that extreme roughness of
the bottom topography may be an unavoidable operating condition, and
there may be a significant number of sites where a "soft rock"
-- machine will be incapable of penetrating the bed material.
The effect on our thinking has been to focus more attention on
the carrier vehicle for the burial unit, and also to consider the
desirability of interchangeable burial units for soft rock and hard
rock.
Personnel at NAVFAC have also been influenced by recent dis-
cussions, and a revised concept guide was issued to CRREL in December.
This document is included here at attachment #1.
Outline of System and Functions
Goal. The goal is to bury undersea cable in various kinds of bed
material, including hard bottom. It is desirable to have a self-
contained machine that can operate across beaches, through the surf
zone, and along the sea bed to the 150 ft water depth. ..
0 S777
~ .~7
. R,.
Operating Options. There are three broad possibilities for laying
and burying cable:
(a) Lay cable first, bury later;
(b) Lay and bury simultaneously;
(c) Trench or bore the bed material first, lay or thread cable later.
This machine is required to bury a number of cables that are
already laid, so that option (a) is required unless the cables are to
be taken up and relaid. However, as far as the design and operation
of the machine is concerned, there need not be much difference between
options (a) and (b).
Functions and subsystems. The burying machine has to provide for a
*number of distinct but interrelated functions, which govern the
design of machine subsystems. The main functions are as follows:
(1) Penetration of the bed material.
(2) Material removal from the trench, tunnel or borehole.
(3) Wall support in the trench, tunnel or borehole.
(4) Laying in the cable
(5) Carriage of the burying unit
(6) Propulsion of the carrier vehicle and burying unit
(7) Power supply
(8) Power transmission
(9) Final drives
(10) Control, guidance and monitoring
For each individual function, a number of concepts are available.However, the chosen concepts for each of the functions have to be -2
mutually compatible when combined into the total system.
ii j" F. IRV
Design Constraints
The system is intended to be operated by Underwater Construction
Teams of Navy Construction Battalions. Preparation, operation and
maintenance should not be unduly complicated.
The equipment has to be deployed at widely scattered sites in
various parts of the world, and there is a requirement for it to be
transportable by C-141 aircraft. It must also be transportable by
road. If the equipment has to be broken into separate modules for %
transport, then preparation and reassembly must be simple procedures
that do not call for special equipment or heavy lifting gear.
The performance required from this system is significantly
beyond the present state-of-the-art, but there is no provision for
R&D. While the complete system will be innovative, it must employ
existing component parts and developed technology.
Although the proposed cable burying operations are not governed
by ordinary economic factors, there are limits to the costs of
acquisition and operation.
Penetration of the Bed Material
There are a number of concepts available for penetrating the bed,
and most of them have been discussed already in the state-of-the-art
assessment. They can be summarized as follows:
A. Mechanical cutting. This covers the use of backhoes, plows, rippers,
disc saws, wheel ditchers, chain saws, ladder trenchers, milling drums,
cutterhead dredges, roadheading machines, impact breakers, percussive6]
drills, vibratory plows, rotary drills, tunnel boring machines, and so on.
4V'N
• .;
_ I ,
B. Fluid jets. For practical purposes this group of concepts is
confined to use of water jets, either with or without entrained solid
particles. It covers continuous jets, pulsed or modulated jets, dis-
continuous slugs, cavitating jets, and jets of sand/water mixtures.
C. Explosive techniques. This covers conventional drill and blast
operations, use of conventional shaped charges, use of flexible linear
shaped charge, gas blasting, special blasting techniques, and innovative
application of liquid and slurry explosives.
D. Exotic methods. This is a catchall category for concepts that are
applicable in principle, but not very promising for the present job.
It covers thermal, electromagnetic and chemical concepts, and the more
* unlikely mechanical concepts, such as free projectile impact.
Material Removal.
Material has to be removed from the furrow, trenchborehole or .ri
tunnel to accommodate progress of the penetrating unit and to permit
entry of the cable. The techniques available can be summarized as
d follows:
A. Direct mechanical transport. This covers devices such as screws,
scrolls, auger flights, conveyor belts, bucket chains, displacement
blades, scrapers, and so on.
B. Fluid transport. This covers movement of solid material as a
fluidized solid, a slurry, or a suspension, using either air or water
as the carrier fluid. It can involve jetting, pumping, or sucking,
either in an open system or in a closed circulation system.
.. . . ,
IrI
4.4.
...- . .-
% N-. /',.S %%' % -"j, s % . , , •• . J _' s " - . . """"": -'•" ' ' "" , r - - . '"""""""-"•" ' " " "
C. Direct lateral displacement. This is applicable to porous materials,
compressible materials, and easily deformable materials. Material from' fNthe trench, furrow, or borehole is pushed laterally to allow the pene-
trating unit to progress.
D. Exotic methods. This is another catchall category to cover methods
that are not likely to be applicable for this job. An example is
material removal by phase change (solution, melting, vaporization).
Wall support
The walls of the trench, tunnel or borehole have to stay apart
long enough for the penetrating unit to pass andr and for the cable
to be laid in. The following possibilities can be envisaged:
A. Competent material - no support needed.
B. Fixed mechanical restraint. This could involve cross-braced sheet-
ing, sheet piling, borehole casing, steel or concrete tunnel lining,
pressure bags, fluid pressure, and such like.
C. Traveling supports. Temporary mechanical support could be provided.04ao dby things like moveable sheeting, tunneling shields, slip forms, or
feed shoes traveling immediately behind the penetrating unit.
D. Ground treatment. This covers grouting, cementation, freezing, and
so on.
Laying in the cable
The main possibilities for laying-in procedure are the following:
A. Payout from a fixed site on the bed or the shore. Cable could be
* laid into open trench directly by bottom pull, or it could be passed
through a feed shoe while fresh cable is drawn to the machine by
1,4 bottom pull.
VA "
%4'.-
* S S 0 0 0A 0" 0.. j..,, , ,.,7 , ., ; . ,.. -..,.."'. -.,. ,,.*.. ,..,, "..4 ,,4-. . .T ". -,% '
B. Payout from a surface vessel or submersible. Cable can be led from
storage reels on a support vessel to the feed shoe of the burial unit, 6-A
or into open trench.
C. Payout from the cable burying machine. Cable can be laid into the .
trench or tunnel from a storage reel on the trenching or boring unit.
D. Pickup of previously laid cable. The burying machine can track along
the line of a previously laid cable, picking it up and feeding into the
bed behind the penetration unit.
Carrier vehicle for the burying equipment.
Some kind of carriage is needed for the burying equipment.
Possibilities include:
A. Sled
B. Tracked vehicle
C. Wheeled vehicle .'i *'
D. Walking machine
E. Bouyant submersible craft N
F. Surface vessel
G. Hybrid device
The carrier has to support the burying equipment as it traverses V.
from the beach, through the surf zone, and over a variety of bottom
conditions. Bed material ranges from very soft sand and mud to hard
rocks. Topography ranges from perfectly flat bottom to extremely rug- V.
ged rocky terrain. The equipment has to withstand waves and currents.
Forces developed by the burying operation itself will probably be trans-
mitted to the carrier.
L L
* 0 9 0 0 0 0 0 0 0 0 0 0 0 0 0
r ,-';S.4"S S S . .. \.'," . .. . . . . . . . . . . . . . . . . . . . . . .L,~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 4,S~ Z . . .. . .... . . . . . . . . . . . . . . . . . . . ..'4 "-" ." "o - ".-.; ""' " " "" ' -> ""- - " " ".' ' 2 . -.- ' -. ' - ' .. ' .'•'
Propulsion of the carrier vehicle and burying unit
When the burying equipment is actually working, it can be pro-
pelled in various ways:
-A. Self-propelled from bed reaction or sidewall reaction. This could 4-
be by wheels, tracks or pads on the sea bed, on the sides of the trench
or bore, or on the pipe or cable that has to be buried. Rolling chains
can be included in this group. Self-propelling cutter units can also
be included.
B. Self-propelled from fluid reaction. This might involve jets,
propellers, thrusters, and such like.
C. Surface tow. This includes towing of the sea bed unit by a
continuously moving surface vessel or by an anchored vessel, using
either a tow cable or a rigid towbar (stinger).
-~~, D. Bottom pull. This includes direct kedging using anchor points
and winches, and also pulling from the beach via direction-changing
sheaves. It can also include arrangements where the carrier moves
intermittently and moves the penetrating unit relative to itself.
E. Direct thrust. This could be applied in rotary drilling.
Power supply
There are two broad oossibilities for location of the power source:
A. Integral power supply. This could be a primary diesel source with
a snorkel, a set of electric storage batteries, fuel cells, or some
more exotic arrangement.
B. External oower supply. With external power supplie4 from the beach
or from a surface vessel, the primary source would almost certainly be
diesel, although there are other possibilities.
A%N 4
4F
,* 0 .- .S5 0 5 5 S
".,W
Power transmission
The first concern here is with power transmission from an external -
power source to the sea bed unit. Excluding exotic and inappropriate
concepts, the possibilities are:
A. Mechanical transmission. This covers machines like conventional
cutterhead dredges, ladder dredgers, rotary drills, surface-towed plows ._-_
and rippers.
B. Hydraulic transmission. Direct hydraulic transmission involves a
pump at the surface power source and hydraulic motors on the sea bed
unit. The umbilical has hydraulic hoses.
C. Electric transmission. This involves an electric power source on
the surface and electric motors on the sea bed unit. The umbilical has
an electrical cable.
D. Pneumatic transmission. This requires a compressor at the surface
and air motors on the bed unit. The umbilical carries air hoses.
* .Final Drives
The final drive outputs to tracks, winches, cutters and so on are
likely to be mechanical. The incoming power from an outside source has
to be transmitted through the sea bed unit, and if necessary converted
to the required mechanical output. Possible systems for converting and
transmitting the incoming power are:
A. Mechanical. This is applicable where power is supplied mechanically.
It may involve gears, drive chains, belts, shafts, rollers, clutches,
and so forth. ''
B. Hydraulic. With an input of hydraulic power, final drives can be
turned by hydraulic motors, either directly or via mechanical components.
-. '
ni .1 S 0 0 00 004
C. Electrical. With an input of electrical power, final drives can
be turned by electric motors, either directly or via mechanical com-
ponents. The electric motors can be of a type designed for direct sub-
mersion, or they can run in a sealed compartment, driving a power takeoff
through a rotating seal.
D. Pneumatic. With an input of compressed air, final drives can be
turned by air motors.
E. Hybrid. The most obvious hybrid system is electro-hydraulic.
Incoming electrical power drives a high voltage motor, which drives a
hydraulic pump, which in turn supplies hydraulic motors. The electric
motor and the hydraulic pump can be run in a sealed compartment, so
that there is no need for waterproofing the motor or for rotating seals.
Control, Guidance and Monitoring
The operations of the carrier and the burying equipment have to be
controlled, the equipment has to be steered along the desired path and
made to avoid extreme obstacles, and continuous checks have to be made
on the performance of the total system and the main subsystems. Possible
arrangements include:
A. Complete local control. This depends on having an operator on or
along side the equipment all the time it is working, either a diver or
a man in a chamber.
B. Complete remote control. This calls for remote control of all major
subsystems, sensing and telemetering of machine operations, and remote
interpretation of sensor signals.
C. Combination of local control and remote control. This can take a
variety of forms, but generally the goal will be to keep the overall
subsystem as simple as possible.
:"k 10
0 0 6 0 0 0 0 0 S S 0%
Selection of Subsystem Concepts
1. Penetration. We obviously have to rule out exotic concepts.
Explosive methods have been ruled out explicitly by NAVFAC, although
we believe that they are well worth considering for very hard rock.
Fluid jets could probably be made to do the job, but power demands would %
undoubtedly be very high, and there would be high risk of operational
problems. We feel that high pressure water jets for underwater rock
trenching should receive some R&D attention, but until an experimental
prototype has been demonstrated on land or under the sea, the concept
cannot be safely applied to an operational system that is required to
employ state-of-the-art technology. This leaves mechanical cutting.
For undersea pipe burial in tough soils, cutterhead machines
seem to be the choice of most designers, and t:Lere is undoubtedly a
possibility of upgrading performance still further by using cutterheads
that are similar to those developed for mining and tunneling in rock.
Cutterheads and milling drums are not well adapted for slicing narrow
slots, but there is a possibility of getting down to trench widths of ..
about I ft. The lateral force problem of slot milling could be overcome
by having two contra-rotating heads traveling in tandem in different
depth ranges, as shown in fig. 1. .*
For trenching in hard ground on land, special modifications are
made to either wheel cutters or chain saws. Wheel ditchers are being
developed for work in permafrost, but so far the performance has not
been outstandingly successful. On a smaller scale, disc saws have
been developed for slot cutting in frozen ground, concrete, and some
rocks. Perhaps the most versatile kind of ditcher for work in ordinary
* 0 0 0 0 0 0 0 0 0 0 0 0 0
7 - -7 .
* .--- ---- ---------------_
7 -- 7 ..- > - . .-..,
--- V- --- - --- - -- 7 2 -4
_ _ _ _ _. .1- .. .-- ._ _ .. .. . .
.. . . _ __ .-- 7 77._ _ __
-. . . ..- .- . .-
-. 7
_____~~~~~~ ___ ___________77 7ij ---
___________f ____ _____ ___ _____
------- - - - : 1c
.1 .-* .
-4 --- 4 -
--
. . -- ,----
soils is the ladder trencher, and this type of machine has been
developed for work in harder materials. However, more robust chain
saws such as those used in the mining industry provide a more suitable
starting point for hard ground trencher development.
Making a choice between the wheel and chain configurations, we
tend to favor the chain. Some of the reasons are as follows:F-
1. For deep digging, wheels are large and cumbersome.
2. Changes in digging depth alter the cutting geometry of a wheel
and change the direction of the resultant axle force very significantly.
3. Cutting teeth on ap upmilling wheel enter the work with almost
zero depth of bite, which tends to enhance wear rates.
0 4. A chain saw can vary the digging depth and the direction of the
resultant force independently.
5. Depth of bite for a cutting tooth on a chain remains more or less 7.[.,
constant throughout the working sweep.
6. A chain has some self-cleaning tendency because of extreme flexure
at the end sprockets.
About the only advantage of a wheel is the fact that it needs
only one bearing, whereas a chain has many bearings and sliding surfaces.
The choice of a chain saw for this task is quite clear cut. It
has the capability of working in both soft bottom and in some of the
weaker rocks, while making only modest demands in terms of power,
traction and reaction. Like any other drag bit device, a chain saw will
not operate economically in very hard rock (say over 20,000 lbf/in2 com-
pressive strength), and it may well show unacceptable wear rates in
rocks of only moderate strength (say over 10,000 lbf/in2).
0
In soft bottom, a chain saw may well be unnecessarily complicated.
Our design will make provision for replacement of the saw with a simple
plow if jobs have to be carried out at sites where there is no hard
bottom.
In very hard bottom, where there are exposures of igneous rocks or
hard metamorphics, the saw will not work. We have a concept for trenching
hard rock with percussive chisel tools, but this is definitely not
state-of-the-art - it calls for R&D effort to develop an experimental
prototype. However, our design will make provision for replacing the
saw with a percussive machine if one becomes available, and if the need
arises.
2. Material Removal. Having selected a chain saw for penetration,
the material removal function will be primarily mechanical with the
cutting teeth sweeping the cutting up to the free surface. There should
be little tendency for cuttings to spill back along the chain, as it is
inducing a water flow in the required direction. If necessary, scraper
blades can be set in among the cutters, but these are not likely to be
needed. For work in sticky clay, a small cleaning jet might be needed
near the upper sprocket.
3. Wall support. The obvious method of providing wall support is by
means of a traveling shield. This can hold the walls apart and keep p
out settling debris until the cable has been laid in. The traveling
shield in this case will be a feed shoe set directly behind the chain
saw. The cable will slide in a smooth curve through a duct inside the
feed show, emerging at the base of the trench cut by the saw.
R, ", -
O 0 0 0 S S 0 5 0 0 0 0 S 0 0 S S
4. Laying in the cable. The immediate requirement is for the equipment
to work at sites where cable is already in position on the sea bed,
so that the machine will track along the cable, picking it up and paying
it into the trench through the feed shoe. For work at new sites, there
are various procedures that can be followed. The only procedure that
our design will not accommodate ip payout of cable from the burying
machine; such a procedure makes very little sense.
5. Carrier vehicles. The extravagant mobility requirements that have
been discussed in connection with this project lead in the direction of a
large complex machine that would in all probability be too expensive for
the project budget, too big to meet the transportation constraints, and
* too complex to suit the operating personnel. Such a behemoth would be
out of proportion to its required function.
We have made an arbitrary decision, and taken what in our judgement
appears to be the best state-of-the-art compromise. We have conceived
a vehicle that has high capabilities for negotiating very rough terrain,
expedient capability in very soft ground, and the ability to carry
required payloads. It is not an ideal carrier for a rock cutting unit,
in terms of compliance, but it should be adequate.
The general idea is to have the carrier behave like a crocodile,
walking over the hard ground and sliding on its belly in the muck.
This can be achieved with a tracked vehicle that has a smooth sled-
like belly. In order to negotiate obstacles and provide stability
with limited vehicle width, an articulated configuration is envisaged.
* 0 0 0 0 0 0 0 0 0 0 0 S S S
% J.. 1 .% %:
.% % % " , % -' -" -" " '
Development of new vehicles is very expensive, and therefore we
propose to assemble the new machine from modifications of well tried
existing vehicles. The cost goal is to rely on basic hardware that
sells for approximately $100K (plus engineering and assembly).
6. Propulsion. Having chosen a tracked carrier, the primary propulsion
will be provided by track shear on the bed. This may be insufficient
for maximum performance trenching in very soft material, when the
carrier vehicle is behaving like a sled. For supplementary traction,
kedging winches will be provided.
7. Power supply. For this application, we can probably reject integral
power supply. The burying machine has fairly high power requirements
(probably over 200 hp), so that electrical storage batteries of the
size that could be carried in a comparatively small vehicle would need
frequent recharging. An internal combustion engine would need a large
snorkel, and a 150 ft high sno, -l would be a real problem in rough seas.
The most reasonable solution seems to be a primary diesel source on the
beach or on a surface vessel.
8. Power Transmission. For power transmission from the external source
to the sea bed unit, the only strong candidates are hydraulic and
electrical systems. In broad terms, high voltage electrical transmission
is effieient and practical over long distances, whereas hydraulic trans-
mission involves heavy losses if long distances are involved. Until the
question of the final drive system is settled and the question of tether
length is finally resolved, we cannot make a proper choice between the
electric and hydraulic alternatives. If a short umbilical is acceptable, J..
(CEL engineers set 600 ft. as a practical limit) then hydraulic trans-
mission may be preferable. Its advantages include diver safety, relative
14.
*O 0 0 0 0 S 0 0 S 0 S 0 0 0 0 S S
• , . •
simplicity (including simplification of final drive), and avoidance of
heat dissipation problems on the sea bed unit. If a long umbilical is
necessary (NAVFAC calls for 2500 ft), then it may be necessary to use
high voltage electrical transmission. To transmit hydraulic power over
long distances it is necessary to either accept heavy losses or use i
large diameter hoses. Large diameter hoses are expensive, bulky and
difficult to manage (a 2500 ft umbilical will add significantly to the
traction requirements of the carrier vehicle).
9. Final drives. The final drive system depends on the main power
transmission system, which so far has not been chosen. However, the
choice is between electrical and hydraulic input. If the incoming
0 power is electric, then the final drive will be either electric or
electro-hydraulic. If the incoming power is hydraulic, then the final
drive will be hydraulic. Track drives can be handled conveniently with
either electric or hydraulic motors, since not much power is needed.
"The cutter drive will consume most of the power - perhaps something
v of the order of 200 hp. The cutter chain will probably run at constant
power or constant torque. It is very likely that hydraulic actuators
will be used on the vehicle articulation joint and on cutter bar "
positioning controls, so that there will be a need for at least some
hydraulic power.
On balance, a pure hydraulic system seems most attractive, with
an electro-hydraulic system as an alternative. A purely electric
system is probably not practical, although direct electric drive of
the cutter is definitely possible.
-AA
%s
Vj A;w7 ;
P4 , - 1- .+n +... ., -+
10. Control, Guidance and Monitoring. Ideally, the burying equipment
' : should have complete automatic remote control. However, complete remote
control of all functions calls for a complex and expensive subsystem.
The prototype of such a system will almost certainly create operation
and maintenance problems for UCT's. Because there are so many uncertainties . ! ,
about more basic subsystems (cutter and vehicle), we feel that it would
be unwise to rely immediately on complete remote control.
Complete local control is the easiest option for a designer, and ]it is certainly a good way of gaining experience with an entirely new
kind of machine. However, when the system is operating smoothly it may
be neither necessary nor desirable to have local control. ii* Taking into account logistic constraints, cost factors, and the
pioneering nature of the project, we opt for a combination of local
control and remote control. Local control would be used for startup
and sumping in, for operation over very rough terrain, for maintenance,
and for overcoming special problems. Remote control would be used
for routine operations with easy bed conditions, and for operation in
hazardous conditions.
To simplify guidance, we favor heavy reliance on route survey,
pre-setting of cable, and placement of suitable bed markers. Some
simple expedients include: (a) properly laid cable (no spaghetti tangles),
(b) optical targets (perhaps with high intensity strobe lights), (c)
V' anchor points for kedging cables. We have reservations about the
.
[II cable-follower devices that have been discussed, since it is desirable
'4
%. . % "v
to have the cutter traveling along straight lines and smooth curves
(not wedeling along the wiggles of the cables). In the first stage of
development, manual remote steering seems preferable to automatic unless
the operating conditions are specially favorable (tracking to a strobe
beacon over smooth bed, kedging to a pre-set anchor point).
Cutting depth on the saw will not be continuously varied, but will
be set at a selected value that can be changed from time to time as
material properties change. This change can be made manually, by either
local control or remote control. A decision to change depth can be
made by direct inspection of the bed material when local control is
being exercised. For remote control, the decision will probably be
based on readings of feed rate and power consumption.
Feed rate (travel speed) ought to be adjusted continuously so as
to draw full cutter power, or some predetermined percentage of full
power that is governed by digging depth (keeping power density approxi-
mately constant). This adjustment can be made manually, or by means of
a servo feedback from the cutter motor to the traction motors or
winch motors.
Bar angle on the cutter will be pre-set and maintained at some '1
selected value.SU
NAVFAC and CEL apparently expect a control to keep the trench
vertical. This can be arranged by a self-plumbing control, but the
effects are not quite as simple as they might seem. There is a possiblity
that a plumbing control might be more bother than it is worth.
' ... .'-.A L- M6 an ILA hL 9
7 7 ... .. .
7T~h~lu ~ ~ - TTT L
. . . . . . . . . . . . . ..... .. . . . . . . . . . .
-- ~~t --.....
C6.
- jo
Ii
___ __? Lt
___ _ _ iJ- .- at --
Summary and Conclusions
We propose that the subsea cable burying machine should have a heavy
duty rock-cutting chain saw followed by a closed feed shoe for laying jin the cable. The equipment can be carried on a two-unit articulated
crawler tractor that has positive control of pitch and yaw. The units
will have smooth belly plates that can function as sleds in soft muck.
N The track system will be a military type for obstacle negotiation,
but it will be stiffly sprung to carry a heavy load and to provide a
stiff reaction to the pulsating cutter forces. Propulsion will be by
tracks wherever possible, aided by kedging winches in difficult con-
ditions. Power will be supplied from an external diesel source
located either on the beach or on a surface vessel. Power transmission
will be either electric or hydraulic, subject to further discussions
with NAVFAC. Final drives will be hydraulic, electric, or electro-
hydraulic. The control and guidance system will utilize both local
control and remote control, and will be the simplest system that is
capable of providing adequate performance. Emphasis will be given to
route selection, pre-placement of cable, and pre-set guidance points.
The problem definition is still inadequate. We are uncomfortable
about the lack of specific site information, and the lack of input
from experienced UCT field personnel. We would draw special attention
to the following points:
1. The requirements levied are beyond the present state-of-the-art. '
2. Variable cutter width is not easy to provide.
F.N -.3. Ideas of combining pipe-burying and cable-burying capabilities in
the same machine are highly questionable unless pipe diameter is limited
*- to a few inches. ' b
-
!, , 7:,
6
4. The requirement for "sidehilling" performance will cause trouble " ".
';" (on steep sideslopes, any vehicle will sideslip slightly, causing the
saw and feed shoe to bind).
5. A minimum umbilical length of 2500 ft limits the options on power
transmission.
6. A 2500 ft umbilical dragged from the beach makes significant traction
demands on the vehicle.
7. It is not clear to us how a burying machine could be operated and
maintained a mile or more from the shore without a surface support vessel.
*[ These matters will be discussed further in the next report.
*%
•V .-
'Vi
.--
[ , "£2.'_..*\" " -.
.'-,.4.".4".-".'..4...,-,. -. , -.:, ,. . . ... , . .. . . .". . " " , " ! "
,¢Z, 3 December 1976
CABLE TP,-.CH.ER
CONC E'PT21 GUIDE FOPR C R""
SU5 SYSTE.MS
I. TRACK CONFTIGURAT:ON
Look at all configuration (1) sing'le pair of tra.:sincluding: (2) two pair of tracks
IN (3) tricycle tr..k* (4) any others .,
Constraints
1. C-141 pavload limit - 70,000 lbs. &' ' . o2. C-141 width limit - 916". ..3. Limit of large crane on beach - 20,000 lbs.4. Se:abee's should not attcmpt assembly on beach fhnich .
-,, technically comolicated or requirs availability anduse of complex or sensitive equip-mnt arid tools.
* 5. Must transit over 2 feet high step olstacle.6. Must transit over loose sand.
7. Must transit over open trench 5 feet across an 3 e .
deep.
IT!. TREN C H -ER
T.avored concept - Laldder.
A.Lso consider others.
Constraints
1. M.ist cut trench 7' (lee.) 12" wide in sand. ust cuCtrench 2 1/2' deep 6" vide Lin coral a n S -f'
2. M.in embedlernt sp.,.ed 5 fp .3. Clttcing teeth .. or in
grouPs (an",....s, a:; en: .. .... "b-
" oel. uha,:.a:nlnc cutt'rn' het cr d. K.a~e
.S L*.4
',. Considc all types including: (1) I y-
(3) E c t ic,_- i_.,
/ 't,\.I ~ .5-45
• • • •• • • •• • • •• •
Constraints
1. Must nrovide support from either b-each or surfaceplatform.
2. Preferable to allow protection of diver from electrical '3Icable break while on machine, operating it during shortemergency periods and during return to beach.
3. Tether from beach - 2,500 feet long minimum.4. Tether from surface platform - 600 feet long minimum.5. Eventual system certification for diver safety must be
considered as influencing any degree of high voltageelectrical usage near diver, even for short periods.
6. Power cable must be capable of connection and dis-connection by diver at trencher at depths of 135 feet.
IV. DRIVE SYSTEM
Consider: (1) Hydraulic(2) Electrical
For hydraulic system, output of transmission must be dividedinto separate circuits of puRups and drive motors. Each hydra-ulic circuit will separately drive each track, trenchingmechanism and the various controls. . .,
Normal operation will be remotely controlled.
Constraints
1. Transit speed on level terrain - 100 fpm.2. Maximum slOpe climbing capability - 450.3. Capable of diver operated local hydraulic control in
emergency.
V. ('C", .... L S'YSTEI
eo iton aill b- rcrate.y controlled. AutomaticI.-" vta to b - resolved.' Cable will b1 lai.d alcn .j
f ur fv an clearQ. route rior to e.>LuIC n t.,* .{-"':O oCL u.dartce oE trencher. LLLT'V with pan and til-
. . n-ec.1rr on trencher tor gencal overall viewing ,,:hen*. t - c '- y permi ts.- Ccmprpas; will be mounted to TV camera
* 0 0 0 0 060 0 0 0 0 0 0
-of-v 'ie )
.
Constraints
1. Must nrovide support from either beach or surfaceplatform.
2. Preferable to allow protection of diver from electricalcable break while on machine, operating it during shortemergency periods and during return to beach.
3. Tether from beach - 2,500 feet long minimum.4. Tether from surface platform - 600 feet long minimum.5. Eventual system certification for diver safety must be
considered as influencing any degree of high voltageelectrical usage near diver, even for short periods.
6. Power cable must be capable of connection and dis-connection by diver at trencher at depths of 135 feet.
IV. DRIVE SYSTEM
Consider: (1) Hydraulic(2) Electrical
For hydraulic system, output of transmission must be dividedinto separate circuits of pumps and drive motors. Each hydra-ulic circuit will separately drive each track, trenching ft 3'mechanism and the various controls.
Normal operation will be remotely controlled.
Constraints
10fm... Transit speed on level terrain - 100 fpm.2. Maximum slOpe climbing capability - 450.3. Capable of diver operated local hydraulic control in
emergency.
V. CONTROL SYSTEM
Ni-rmal ooeration will b-: .. n - ely iC- vcrsus .-.,n:al yct to b- resolved. Cabhe will > 1;0 id alornj
pr'vi.).;iy surveycd an' cleare, route nrior to eaa 1ail .lt for gLidance o .... ...nchc-r . L ....- in a- ti1twill be mountecd on trencher for g .. r... I whnw-tar clarity permits. Compass will b,. ounted to TV camera:;:L hinF% (Ticld-of-viw .4
r 'A• •
S g 6 40 0 0 0 0 0 0 0 0 0 0
WflWWWSLZ
0
0
0
1-IC